2015-03-31T18:06:41ZThe irregular firing properties of thalamic head direction cells mediate turn-specific modulation of the directional tuning curve.http://hdl.handle.net/2262/73411
The irregular firing properties of thalamic head direction cells mediate turn-specific modulation of the directional tuning curve.
O'MARA, SHANE MICHAEL; REILLY, RICHARD
HEAD DIRECTION (HD) cells in anterior thalamus express a wide range of interspike intervals (ISIs) (Taube 2010). Given the importance of HD encoding for spatial navigation in the environment, it is crucial to understand whether intrinsic biophysical properties mediate the shape of directional tuning curves. Here we ask how ISI patterns affect the formation of the HD tuning curve in the horizontal plane. ISI variability is evaluated by the coefficient of variation; high values reflect an irregular pattern of the spikes (Softky and Koch 1993). ISI variability is very sensitive to the mean firing rate (Holt et al. 1996; Softky and Koch 1993); however, large ISIs as part of intertrain analyses are not simply noise around the mean firing rate but reflect characteristics of the membrane potential (Angelo and Margrie 2011). To investigate the functional relation between ISI diversity and separation angle, we use a single-cell Hodgkin-Huxley-type model to simulate ISI patterns ranging from irregularly to regularly firing-type cells (Pospischil et al. 2008). We apply sinusoidal current injection that mimics the Gaussian distribution of HD signal in thalamic neurons (Taube et al. 1990). Experimental and theoretical evidence suggests that bursts occur preferentially on the ascending slope of input signal (Gabbiani et al. 1996; Guido et al. 1992; Kepecs et al. 2002). Thus irregularly spiking neurons may detect the rising slope of input signals with greater precision compared with regularly spiking neurons (Metzner et al. 1998; Sherman 2001).
PUBLISHED
2014-01-01T00:00:00ZRespiratory cycle entrainment of septal neurons mediates the fast coupling of sniffing rate and hippocampal theta rhythm.http://hdl.handle.net/2262/73410
Respiratory cycle entrainment of septal neurons mediates the fast coupling of sniffing rate and hippocampal theta rhythm.
O'MARA, SHANE MICHAEL; REILLY, RICHARD
Memory for odour information may result from temporal coupling between the olfactory and hippocampal systems. Respiration
defines the frequency of olfactory perception, but how the respiratory rate affects hippocampal oscillations remains poorly under-
stood. The afferent connectivity of the medial septum/diagonal band of Broca complex (MS/DB) proposes this region as a cross-
roads between respiratory and limbic pathways. Here we investigate if the firing rates of septal neurons integrate respiratory rate
signals. We demonstrate that approximately 50% of MS/DB neurons are temporally correlated with sniffing frequency. Moreover,
a group of slow-spiking septal neurons are phase-locked to the sniffing cycle. We show that inter-burst intervals of MS/DB theta
cells relate to the sniff rate. Intranasal odour infusion evokes sniff phase preference for the activity of fast-spiking MS/DB neurons.
Concurrently, the infusion augments the correlation between sniffing and limbic theta oscillations. During periods of sniffing
–
theta
correlation, CA1 place cells fired preferentially during the inhalation phase, suggesting the theta cycle as a coherent time frame
for central olfactory processing. Furthermore, injection of the GABAergic agonist muscimol into medial septum induces a parallel
decrease of sniffing and theta frequencies. Our findings provide experimental evidence that MS/DB does not merely generate
theta rhythm, but actively integrates sensorimotor stimuli that reflect sniffing rate. Such integration may provide temporal oscilla-
tory synchronisation of MS/DB-innervated limbic structures with the sniffing cycle.
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2014-01-01T00:00:00ZDecoding signal processing in thalamo-hippocampal circuitry: Implications for theories of memory and spatial processinghttp://hdl.handle.net/2262/73409
Decoding signal processing in thalamo-hippocampal circuitry: Implications for theories of memory and spatial processing
O'MARA, SHANE MICHAEL
A major tool in understanding how information is processed in the brain is the analysis of neuronal output at each hierarchical level through which neurophysiological signals are propagated. Since the experimental brain operation performed on Henry Gustav Molaison (known as patient H.M.) in 1953, the hippocampal formation has gained special attention, resulting in a very large number of studies investigating signals processed by the hippocampal formation. One of the main information streams to the hippocampal formation, vital for episodic memory formation, arises from thalamo-hippocampal projections, as there is extensive connectivity between these structures. This connectivity is sometimes overlooked by theories of memory formation by the brain, in favour of theories with a strong cortico-hippocampal flavour. In this review, we attempt to address some of the complexity of the signals processed within the thalamo-hippocampal circuitry. To understand the signals encoded by the anterior thalamic nuclei in particular, we review key findings from electrophysiological, anatomical, behavioural and computational studies. We include recent findings elucidating the integration of different signal modalities by single thalamic neurons; we focus in particular on the propagation of two prominent signals: head directionality and theta rhythm. We conclude that thalamo-hippocampal processing provides a centrally important, substantive, and dynamic input modulating and moderating hippocampal spatial and mnemonic processing
IN_PRESS
2015-01-01T00:00:00ZEmployment and vocational skills among individuals with autism spectrum disorder: predictors, impact, and interventionshttp://hdl.handle.net/2262/73402
Employment and vocational skills among individuals with autism spectrum disorder: predictors, impact, and interventions
LYDON, SINEAD; HEALY, OLIVE
Much research has been devoted to early intervention for individuals with Autism Spectrum Disorder (ASD), with a lesser emphasis on research examining the outcomes for, or support of, these individuals as they reach employment-age. Historically, employment opportunities for individuals with ASD have been limited. The current literature review sought to investigate the existing predictors and impact of employment or vocational placements among persons with ASD. Interventions described in the literature to teach individuals with ASD employment or vocational skills were also assessed. A total of 26 studies were reviewed and results indicate that there is limited extant research on employment and vocational skills among individuals with ASD. However, it was found that employment positively impacted on the quality of life, cognitive functioning and well-being of participants with ASD. Predictors of employment were found to be a complex interplay of personal and external factors. All interventional studies reported improvements in the vocational skills targeted although a limited range of skills have been taught across these studies. The implications of these findings for individuals with ASD and future research in this area are discussed.
PUBLISHED
2014-01-01T00:00:00Z